The US Govt link is:
http://travel.state.gov/passport/get/re ... w_833.html
They say
"Residents abroad should renew their passports at nearest U.S. Embassy or U.S. Consulate. "
The CR website says
http://usembassy.or.cr/uspassport.html (excerpt below)
It doesnt have online forms etc. So you can do the waiting game here or use one of the expedited visa stetside
U.S. Citizen Passport Processing
All American citizens residing or traveling abroad who require issuance of a U.S. passport will be issued the latest, state-of-the-art passport incorporating a photo-digitized image and other enhanced security features.
U.S. Embassies and Consulates will achieve this goal by transferring the passport issuance function to a domestic U.S. passport facility. This will increase processing time at some U.S. Embassies and Consulates, but the Department of State is committed to ensuring that American citizens receive secure documents in a timely manner. American citizens are encouraged to apply early for renewal of expiring passports.
U.S. Embassies and Consulates will continue to issue passports in emergency cases. Such passports will be limited in validity, and cannot be extended. Bearers will be required to exchange their limited validity passports for a full-validity photo-digitized passport upon completion of their emergency travel, either through a passport facility in the U.S. or the U.S. Embassies or Consulates abroad.
As of April 8, 2002, overseas posts are no longer authorized to issue full-validity passports. Please be advised that all non-emergency passport applications must be sent by the Embassy to the National Passport Center for printing, and may take up to two weeks to be returned to the U.S. Embassy, San Jose, for retrieval by the applicant.
Additional information regarding the new application procedure will be provided as soon as it becomes available.